PET resins and polycarbonate resins are typical materials for stretch blow molded articles and direct blow molded articles. However, these resins are heavy with a specific gravity of 1.2 or more, and are also unsuitable for the recent need of volume reduction and the international issue of preservation and consumption reduction of oil resources. Accordingly, new materials have been demanded.
Polypropylene resins are generally excellent in chemical properties, physical properties and forming properties and are inexpensive. They are therefore used in various applications including food containers and medical containers. However, the polypropylene resins themselves do not always satisfy desired transparency or mechanical strength. Accordingly, the resins are usually blended with nucleating agents to achieve improved transparency or mechanical strength.
For example, the transparency of propylene/ethylene copolymers is enhanced by adding a nucleating agent or increasing ethylene incorporation. However, increasing the ethylene content results in more extracts to cause various problems in the forming process. Further, nucleating agents added to general polypropylene resins do not provide clear transparency due to crystallinity.
Furthermore, polypropylene resins blended with conventional nucleating agents show a clear melting point and a narrow melting point range. As a result, moldability in stretch blow molding and direct blow molding is lowered and the production stability is deteriorated.
These problems are addressed in JP-A-2003-286377, JP-A-H11-255982 and JP-A-H10-152530. These documents aim to improve moldability by distributing melting points so that the material is characterized by having two different peaks of melting points. In these circumstances, there is a need for polypropylene resins that are easily blow molded and are capable of giving molded articles having excellent transparency, impact resistance and flexibility.
Patent Document 1: JP-A-2003-286377
Patent Document 2: JP-A-H11-255982
Patent Document 3: JP-A-H10-152530